Preheat oven to 350°F. Coat a 9×9 baking dish with nonstick spray. Set aside.
Combine melted butter, brown sugar, cinnamon, salt, flour, and pecans in a medium bowl. Stir until evenly combined. Set aside.
In the bowl of your stand mixer fitted with the paddle attachment mix the butter and the sugar together on medium speed for 2 minutes. Add in the eggs and continue mixing on medium for 2 more minutes, scraping the sides of the bowl as necessary.
Add in the vanilla, sour cream, salt, baking powder, and baking soda. Mix for 1 minute until combined.
Turn the mixer to low and add int he flour until just combined. Don’t over mix.
Spread half of the batter in the bottom of the pan. Sprinkle half of the streusel mixture on top of the batter. Carefully spread the remaining batter on top of the streusel, spreading it out with a spatula or offset spatula. Sprinkle the remaining streusel on top.
Bake for 30-35 minutes.
Whisk together the powdered sugar and milk until no lumps remain. Drizzle this on top of the cake while warm.